In the related art, a method has been known, which connects contact points of a plurality of relays in series and multiplexes the contacts by considering failures of the contact points to improve operation reliability of an interruption control of an electric circuit.
That is, in an international standard associated with machine safety, a basic safety principle is not to control opening/closing of two contact points at the same timing with respect to two contact points connected in series in order to ensure an interruption control of the electric circuit (ISO 13489-2: 2003). Therefore, two contact points are divided into a contact point applied with an electric load and a contact point which is opened/closed in a no-current state, and even when a welding failure of the contact point occurs at the contact point applied with the electric load, the welding failure is prevented from occurring at the contact point which is opened/closed in the no-current state and the electric circuit is significantly interrupted by the contact point where the welding failure does not occur.
Meanwhile, Patent Documents 1 and 2 disclose a relay that assures that a predetermined contact point is opened when the welding failure occurs at the contact point by coupling an operating member to a contact spring by using a forcing guide contact mechanism. A method example that performs a control for warning or safety after the welding failure of the contact point occurs by using the specific contact point (examination contact point) is also disclosed in Patent Documents 1 and 2.
Further, Patent Documents 1 and 2 illustrate as an embodiment even two contact points in the same relay which are opened/closed at an earlier timing than a check target contact point when the contact point is opened and at a later timing than the check target contact point when the contact point is closed at a contact point operated similarly as a contact point which is the target for checking the welding failure, and disclose an application to a measure for preventing power from being reinput into a motor, and the like. According to the invention disclosed in Patent Documents 1 and 2, safety can be improved by preventing the power from being reinput into various apparatuses when an error occurs. Further, Patent Document 3 proposes the invention associated with application and use of the examination contact point.    Patent Document 1 Japanese Patent Application Publication No. 7-70283    Patent Document 2 Japanese Patent No. 2584399    Patent Document 3 Japanese Patent Application Laid-Open No. 2003-140702